March 25, 2012
Study Discovers How Massive Black Holes Grow So Rapidly
Black holes that grow to masses billions of times greater than that of our sun most likely reached those sizes by consuming objects from multiple locations at the same time, researchers from the UK and Australia claim in a new study set for publication in the journal Monthly Notices of the Royal Astronomical Society.
In a Friday press release, officials with the University of Leicester, who conducted the study along with colleagues from Australia's Monash University, compared the process to that of eating a meal -- only in this case, the black holes "have no ℠table manners´, and tip their ℠food´ directly into their mouths, eating more than one course simultaneously."
While it was believed that the black hole was surrounded by one gas-and-dust ring, known as an accretion disc and formed from nearby planets and stars pulled in by the black hole's suction forces, the researchers in this new study created a model that suggested that there may, in fact, be more than one accretion disc.
"The researchers did computer simulations of two gas discs orbiting a black hole at different angles and found after a short time the discs spread and collide, and large amounts of gas fall into the hole," UPI reporters wrote on March 23, adding that lead researcher Andrew King of the University of Leicester and his associates reported that their calculations showed that black holes can grow up to a thousand times faster when this phenomenon occurs.
King's research, which was funded by the UK Science and Technology Facilities Council (STFC), looked at some of the largest black holes in the universe, including ones about "a thousand times heavier" than the one at the center of the Milky Way, which itself is approximately four million times heavier than the sun.
"We know they grew very quickly after the Big Bang," King, a professor from the university's Department of Physics and Astronomy, said in a statement. "These hugely massive black holes were already full -- grown when the universe was very young, less than a tenth of its present age."
"We needed a faster mechanism," added Chris Nixon, also of the University of Leicester, “so we wondered what would happen if gas came in from different directions.”
Thus, King, Nixon, and Australian associate Daniel Price created their computer simulation, learning that if two gas discs orbit a black hole at different angles, they eventually spread and collide, dumping massive amounts of gas into the hole. King said it was comparable to the loss of centrifugal force that occurs when two motorcycle riders collide while riding on a "Wall of Death."
"We don't know exactly how gas flows inside galaxies in the early universe, but I think it is very promising that if the flows are chaotic it is very easy for the black hole to feed," he added.
Image Caption: English: This artist´s impression depicts the newly discovered stellar-mass black hole in the spiral galaxy NGC 300. The black hole has a mass of about twenty times the mass of the Sun and is associated with a Wolf—Rayet star; a star that will become a black hole itself. Thanks to the observations performed with the FORS2 instrument mounted on ESO´s Very Large Telescope, astronomers have confirmed an earlier hunch that the black hole and the Wolf—Rayet star dance around each other in a diabolic waltz, with a period of about 32 hours. The astronomers also found that the black hole is stripping matter away from the star as they orbit each other. How such a tightly bound system has survived the tumultuous phases that preceded the formation of the black hole is still a mystery. Credits: ESO/L. CalÃ§ada